In next-generation multi media mobile communication which is recently being researched and developed briskly, it is necessary to integrate various systems such as an individual mobile phone, a radio pager, a mobile data, a satellite communication, and etc., and thereby to provide an international roaming which enables users to communicate with whoever, wherever, and whenever. In addition, it is aimed to provide a multiple information service in which voice, data, image, and etc., are integrated.
In order to provide a multi media communication service in mobile communication, a high speed transmission and various type of data transmission are needed, so it is essential to increase an efficiency of a system by using different encoding schemes according to types of channel and data.
Meanwhile, when transmitting data, a portable Internet system uses a 2.3 GHz bandwidth, adopts an orthogonal frequency division multiplexing access (OFDMA) scheme, and uses a time division duplex (TDD) scheme in switching an uplink and a downlink during 5 ms. The downlink has a packet length of 24,000 bit, which is a rather long data packet length. In order to efficiently perform a channel decoding for such a long data length, a LDPC coding scheme is advantageous.
In the 1960's, Gallager invented the LDPC code for an LDPC encoder. The LDPC code shows better performance than the conventional turbo code. According to the LDPC code, complexity of a decoder is low, a parallel operation and a high speed process are possible, and an iterative decoding scheme may be applied like in a turbo decoder. So, it is appropriate for the mobile communication system in which a low error rate and a high speed data process are required.
According to the international standard IEEE802.16e, a convolutional turbo code (CTC) encoder is basically used for a channel coding, and a LDPC encoder is alternatively used, so that it may complement the performance. Korean Patent Publication No. 2004-0044590 discloses about the LDPC encoder. However, hardware of the LDPC encoder is generally more complex than that of the CTC encoder. High complexity of an encoder of LDPC code causes a difficulty in embodying the encoder.
LDPC code has two kinds of H matrix that function as a parity check matrix. Among the two kinds of H matrix, one is a matrix which has binary elements, and the other has non-binary elements.
The H matrix formed of non-binary elements shows better performance than that of binary elements, but it has drawbacks in that a Galois field operation is complicated. On the other hand, the LDPC code of which the H matrix has binary elements (i.e., 0 or 1) may be divided into a regular LDPC code of which rows have equivalent weights and an irregular LDPC code of which rows have non equivalent weights.
In the regular LDPC code, it is not easy to generate a H matrix due to a limitation in making weights of rows be equivalent. On the contrary, in the irregular LDPC code, the weights of rows in the H matrix are not constant, therefore the irregular LDPC code has a merit in easily generating a H matrix formed of high girth (minimum cycle without 4-cycle) determining decoding performance. The irregular LDPC code generally shows better performance than the regular LDPC code. However, it has drawbacks in that the complexity of an LDPC encoder and a decoder which need to have image information of the H matrix is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore, it may contain information that does not form the prior art that is already known in this country to a person or ordinary skill in the art.